Atmospheric Aerosols as Indicators of Global Biogeochemical Changes

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Atmospheric Aerosols as Indicators of Global
Biogeochemical Changes
Rudolf Husar
Washington UniversitySt. Louis, USA
Draft Presentation Prepared for the Induction
into the Hungarian Academy of Sciences
Budapest, June 23, 1998
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The Physiology and Health Care of the Earth System

• The physicians evaluate a patients health by
  measuring the temperature, pulse rate, the
  cholesterol level and other vital signs. For
  diagnosis, doctors use many tools, like x-ray
  images, ultrasound scans, usually in combination.
• The Earth is also like a living organism.
  According to the British scientist James
  Lovelock, it has become necessary to monitor the
  health of planet Earth.
• Today's earth scientists evaluate the physiology
  of planet earth also by monitoring the
  temperature, carbon dioxide, ozone, biomass,
  cloudiness, and many other parameters as the
  vital signs of the interconnected Earth System.
• The observational instruments of earth sciences
  include thermometers, chemical sampling analysis
  of air land and water, as well as earth
  observing satellites.

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Response to Environmental Changes
The physical and chemical state of the Earths
environment is constantly changing. The Earth is
physically aging, and at the same time evolution
is changing the biosphere. Some of the changes
occur slowly in a steady fashion and they are
foreseeable. However, many bio-geochemical
changes occur quickly, unexpectedly, and they
unevenly distributed in space and time. From
human point of view, many of these changes are
catastrophic events. The inevitable and
unforeseeable environmental changes require the
following major steps

• Sensing and recognition of the changes
  (monitoring).

• Explaining of the causes of the changes
  (science).

• If necessary, act in response to these changes
  (management).

Some refer to the above three steps as necessary
conditions for sustainable development. This is
logical since all living organisms use this type
of sensory feedback to maintain their
existence. Sensory feed back

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Major Biogeochemical Processes Visualized by
Aerosols
Dust storms
Fires
Volcanoes
Anthropogenic pollution
Dust storms, forest fires, volcanic emissions and
anthropogenic fuel combustion are major
biogeochemical processes that cause the flow of
substances on Earth. Furthermore, these processes
are producing visible aerosols in form of dust,
smoke, and haze. The quantity and
spatial-temporal distribution of dust and smoke
and haze can be used to characterize the flow of
substances through the atmosphere.
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Just like the human eye, satellite sensors detect
the total amount of solar radiation that is
reflected from the earths surface (Ro) and
backscattered by the atmosphere from aerosol,
pure air, and clouds. A simplified expression
for the radiation detected by a satellite sensor
(I/Io ) is
Satellite Detection of Aerosols
I / Io Ro e-? (1- e-?) P
where ? is the aerosol optical thickness and P
the angular light scattering probability.
Currently, satellite sensors can detect different
aspects of aerosols over the globe daily. Polar
orbiting sun synchronous satellite always views
the sunny side of the Earth. Geo-synchronous
satellite always observes the same location on
Earth.
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Earth in Balance, Earth Changing
The basic elements of life including carbon,
nitrogen, phosphorus, calcium are in constant
circulation between the earths major
environmental compartments atmosphere,
hydrosphere, lithosphere, and biosphere. These
earths compartments remain in balance as long as
the rate of flow of matter and energy in and out
of the compartments is unchanged. On the other
hand, changes in the environmental compartments
will occur if the circulation (in and out flow)
of the substances is perturbed. For example, the
concentration of atmospheric carbon dioxide in
the atmosphere has been increasing because the
rate of input is larger than the rate of output
from the atmosphere.
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Dust Storms
Dust storms are responsible for the transport of
Aeolian dust from one part of the Earth to
another. Loess, the fertile silty yellowish brown
soil, covers about 10 of the land surface of the
Earth. In China, for example, 100 meter deep
layers of loess are found.
The dust particles are removed from the surface
of sand dunes by the force of the wind. The
chemical composition of the dust is similar to
the composition of the sand.
The source areas of loess are the hot and
temperate deserts.
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Sahara Dust Over the Atlantic
The smaller dust particles in the size range 1-5
mm are transported several thousand kilometers
from their source. For this reason, large
quantities of Sahara dust can be found in South
America and east Asian dust over North America
and Greenland.
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Dust as Drought Indicators
Monitoring the atmospheric dust concentration and
dust flow, allows the estimation of the magnitude
of the Aeolian dust transport, drought
conditions, desertification and other changes
occurring over arid regions.
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Fires
Vegetation fires are important to the ecology of
many terrestrial systems because they cycle many
trace elements. Fires are also major sources of
atmospheric trace gases and aerosols. Nowadays
vegetation fires are initiated mostly by humans
for land clearing, agricultural harvest clearing,
savanna burning for nomadic agriculture.
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Smoke from Biomass Burning
The monitoring of smoke aerosol from forest,
grass, and agricultural fires can reveal the
location, magnitude, and seasonality of biomass
burning.
The sub-Sahara savanna region has thousands of
small fires every year in the December-February
season. It produces a thick and rather uniform
smoke layer of several thousand kilometer size.
The prevailing wind transport the smoke across
the Atlantic Ocean to South America.
Occasionally, the savanna smoke and the Sahara
dust clouds overlap. The main atmospheric
removal mechanism of the smoke, dust, and haze
is through clouds and precipitation.
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Volcanic Aerosol

• Volcanic aerosols are composed of grayish
  volcanic ash which settles out within a day or
  less.
• The lasting volcanic aerosol (0.5-1 µm) is due to
  sulfuric acid that is formed in the stratosphere
  from the emitted SO2 gas

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Volcanic emissions tend to spread out through
both the northern and southern Hemisphere and
reside in the troposphere for 1-2 years.
Volcanic events are not influenced by human
actions but they tend to mask out more subtle
changes man-induced changes.

• History of volcanic aerosol optical depth,
  1850-1900 shows sporadic events several times a
  century.
• By monitoring the pattern of volcanic aerosols
  one can determine the magnitude and spatial
  impact of volcanic events.

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Anthropogenic Fuel Combustion
Since the last century human activities have
significantly influenced the Earths
biogeochemical balance. The combustion of fossil
fuels, coal, oil and gas has liberated large
quantities of carbon, sulfur, and trace metals
from its long term lithospheric reservoir and
transferred it to the atmosphere..
In North America, the per capita sulfur emission
is 1/2 kg per day. This large quantity of
mobilized sulfur not only pollutes the air, but
after deposition may acidify the soil, and may
harm the plants.
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Anthropogenic Pollution
Central Europe
India
China
Eastern U.S.
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The 1998 Asian Dust and the Central American
Smoke Events

• In the spring of 1998 two major tropospheric
  aerosol events occurred that illustrate the
  global/continental-scale transport, as well as
• The utility of satellites to detect and to track
  the aerosol clouds
• The support of the scientific community to aid
  the air quality management on short notice.

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The Asian Dust Event of April 1998
On April 15th, 1998 an unusually intense dust
storm began in the western China, just in time
for the east Asian dust season. CNN reported
that 12 people were missing in the storm. By the
April 20th, the elongated dust cloud covered a
1000 mile stretch of the east coast of China.
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Transport over Pacific
Between April 20rd and 25th, the dust cloud was
rapidly moving across the Pacific Ocean. It
appeared as a yellow dye on SeaWiFS satellite
images visualizing its own path across the
Pacific.
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Impact of Asian Dust on North America
By April 27th, the dust cloud rolled into North
America. Goes-10 and SeaWiFS images indicate
that the dust plume split once it reached land -
one branch heading southward along the California
coast and another branch continued eastward
across the Canadian Rockies. During the dust
event the PM10 and PM2.5 concentrations in
Washington state reached 120 and 40 mg/m3,
respectively.
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Science Support to Air Quality Management

• A few scientists were monitoring Asian dust
  event.
• As the Asian dust approached the Pacific Coast of
  North America, air quality managers and other
  scientists were alerted.
• Within two days, over 40 scientists and managers
  have reported their observations and preliminary
  data on the web.
• The air quality managers used the science website
  to inform the public.

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Forest Fires over Central America
Throughout the spring of 1998, thousands of fires
in Central America have been burning with twice
the intensity of normal springtime fires. Thick
smoke has been lingering over southern Mexico,
Guatemala and Honduras and adjacent oceans
throughout the spring season. Several times the
smoke has drifted northward into the USA and
Canada and caused exceedances of the PM standard,
health alerts, and impairment of air traffic due
to thick haze.
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Smoke passes over Eastern North America.

• On May 12, a remarkably thick pall of smoke has
  accumulated over the entire Gulf of Mexico and
  begun a swift journey to the north along the
  Mississippi Valley. By May 15, the smoke pall had
  stretched out from Central America Hudson Bay.
  Over the next two days the smoke pall was
  literally shoved eastward by an approaching cold
  front, resulting in a remarkable contrast of
  haziness (smokiness) in the front and behind the
  front. On May 17, virtually the entire Eastern
  Seaboard was blanketed by a pall of smoke.

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SeaWiFS View of the Smoke

• GOES 8 View of the Smoke

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Science - Management Interaction Regarding the
Central American Smoke Event

• The Central American fires have been keenly
  monitored by broad scientific community using
  multiple satellite sensors.
• The available on-line data were catalogued and
  summarized on the web.
• The local air quality data along with regional
  summaries were used by air quality managers to
  issue health advisories.
• The regional summaries were used by the federal
  EPA to grant the states exemptions from air
  quality standard violations.
• The Asian dust and the Central American smoke
  event has clearly demonstrated that the available
  current space-based aerosol monitoring data can
  enable virtual communities of scientists and
  managers to detect and follow major aerosol
  events and to support air quality management
  through JITERS (Just In Time Environmentally
  Relevant Science).

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Summary Aerosols as Biogeochemical Indicators

• Aerosols are suitable indicators of dust
  movement, fire and smoke, volcanic emissions and
  anthropogenic fossil fuel combustion. Each
  source type has a unique signiture either in size
  distribution, chemical composition, or optical
  properties.
• Aerosols can be easily detected because they
  effectively scatter visible light from the sun.
• Space-based aerosol monitoring systems already
  exist to monitor the daily aerosol pattern
  globally.
• The main problems arise from the fact that the
  remote sensor are retrieving only integral
  properties. Aerosols are also highly variable in
  space, time, optical properties. It takes many
  different high resolution sensors to fully
  characterize global distribution. Lastly,
  multiple aerosol types may coexist at any
  location.

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Recommendations Global Aerosol Watch with GAIN
We recommend the establishment of an
internet-based global aerosol watch system, where
a few experienced observers distributed all over
the world would monitor the daily aerosol pattern
for interesting dust, smoke, or haze aerosol
events. They would utilize the publicly
available on-line satellite, surface monitoring,
and meteorological modeling data provided by many
countries. When an interesting event would occur,
the relevant science and management communities
would be alerted through a Global Aerosol
Information Network (GAIN). Given the alert the
communities could initiate more intense
monitoring and/or prepare the public for the
developing risks. The GAIN system would also be
used for communication and sharing of
internet-based information resources.
Biomass burning - biogeochemists
Aeolian dust - geologists
GAIN Global Aerosol Information Network
Vulcanologists
Radiative effects-Climate Change
Pollution monitoring- Control
Health effects
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Acknowledgements
This is to express my deep appreciation to my
wife Janja who has supported every aspect of this
work. Our son Attila has processed the first set
of global oceanic aerosol maps. Our daughter
Maja has maintained the Asian-Dust
website. Special thanks are directed to the
web-based virtual communities on Asian dust and
Central American smoke. Their willingness to
share raw data sets a great example for future
spontaneous collaboration. This research was
supported by the U.S. Environmental Protection
Agency.
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Human actions have also been altering some of the
main natural biogeochemical processes. The
enhaced intentional burning of forests has
increased the flow of biological substances over
many parts of the world. The spreading of
deserts due to desertification is also likely to
influence the flow of windblown dust.